1. Field of the Invention
The present invention relates to an MRAM (Magnetic Random Access Memory) having a magnetoresistive element and a data write method for the magnetic random access memory.
2. Description of the Related Art
In recent years, an MRAM (Magnetic Random Access Memory) using a TMR (Tunnel Magneto-Resistance) effect has been proposed as a kind of semiconductor memory.
In the memory cells of an MRAM, an MTJ (Magnetic Tunneling Junction) element serving as an information storage element is formed at the interconnection between a bit line and a word line. In a data write mode, a current is supplied to each of a selected bit line and a selected word line. Data is written in the MTJ element of the selected cell located at the intersection between the selected bit line and the selected word line by a composite magnetic filed generated by the currents. In a data read mode, a read current is supplied to the MTJ element of a selected cell so that “1” or “0” data is read out in accordance with a resistance change in the magnetized state of the MTJ element.
In the data write mode of such an MRAM, a write current magnetic field may affect even semi-selected cells selected by one of the selected bit line and selected word line to cause a write error in the semi-selected cells, i.e., rise a problem of disturbance. Avoiding this disturbance problem is being considered as one of most important challenges in MRAM development. However, the shape of an MTJ element and the like sensitively affect the asteroid characteristic. For this reason, the influence on the asteroid characteristic further becomes large as the element size decreases. This may increase write errors in semi-selected cells and make the disturbance problem more serious along with the size reduction of elements. To avoid this problem, the write current must be made large not to cause any write error in semi-selected cells. There is a toggle type MRAM using a recording layer having a multilayered structure with weak coupling. Even in this type, the write current value becomes large.
Prior-art references associated with the present invention are as follows.
[Patent reference 1] Jpn. Pat. Appln. KOKAI Publication No. 2002-299574
[Patent reference 2] Jpn. Pat. Appln. KOKAI Publication No. 2003-163330